1. Field of the Invention
This invention relates to electrostatic field detection systems and more particularly relates to apparatus for panoramically sensing and monitoring electrostatic fields oriented about a 360.degree. arc with respect to the site of the detection device. The instant invention generally pertains to mechanical modulation systems and is especially concerned with a panoramic sensor in which a rotary chopper is interposed between a stationary circumferentially apertured housing and a fixed centrally disposed field detecting element.
2. Prior Art
Almost all systems for detecting and continuously monitoring electrostatic fields include mechanical modulation arrangements. Sensing electrodes convert the electrostatic field or surface potential being monitored into an AC voltage, the magnitude of which is proportional to the detected field or potential. This conversion is accomplished by a capacitive modulation process in which the capacitive coupling between the sensing electrode and the ambient electrostatic field is modulated or varied mechanically at a fixed periodic rate. In some of the prior art field sensing devices, the electrostatic field being monitored passes through a slotted disk or rotary chopper blades, the field being interrupted as ground segments and open segments alternately pass in front of one or more sensing electrodes. See U.S. Pat. No. 3,846,700 or No. 4,055,798 wherein the sensing electrodes behind the disk or chopper produce an electrical signal output when the field falls on the sensing plates and a reverse electrical signal output when the field is interrupted by the disk or chopper. The intensity of the field is related to the amplitude of the output signal and the polarity of the field may be indicated by the phase of the output signal. Another type of field sensor, such as shown in U.S. Pat. No. 4,205,267, utilizes an electrode which is contained in a windowed housing and is itself mechanically vibrated in a plane parallel to the test surface so as to expose the sensing electrode periodically to the field through the window. Still another system, such as is illustrated in U.S. Pat. No. 3,370,225, employs a fixed electrode behind an apertured housing and includes a shutter mechanically vibrated in a plane parallel to a fixed electrode.
However, in none of the foregoing systems are the devices capable of continuously monitoring and sensing panoramically electrostatic fields disposed circumferentially about 360.degree. of arc around the site of the sensor itself. While it is conceivable that the prior art unidirectional detecting devices could be mounted on a rotating platform to measure the electrostatic fields in azimuth, there is no suggestion in the prior art to accomplish that purpose, and it would require expensive auxilliary turntables to achieve such a result. For example, where work is being performed in a room where minimal electrostatic charging environment is required, it is desirable to monitor all areas of that room to insure that personnel or articles entering the area from any part of that room and carrying charge be detected immediately and neutralized as quickly as possible by static elimination equipment.